1. Field of the Invention
This invention relates to a unitized seal assembly of the type used for retaining lubricating grease or oil in a sealed bearing assembly and more particularly to such a seal assembly especially suitable for medium and heavy duty applications such as truck wheel bearings or the like where retaining adequate lubrication in the bearing and excluding foreign matter from the bearing lubrication over long periods of time in adverse operating conditions is critical.
2. Description of the Prior Art
Unitized bearing seals are well known and have been used widely in a variety of applications. Such seals are especially well adapted for use in connection with rail car wheel bearings, truck, trailer and bus wheel bearings, and shaft or wheel bearings for heavy machinery and equipment generally. Seal assemblies of this type normally employ a casing including a first rigid metal case ring structure carrying an elastomeric sealing element and a second rigid metal case ring providing a sealing surface contacted by the sealing element to form the primary lubricant seal.
It is well known that the ingress of contaminants, especially dust or grit and water, past a primary seal lip into the bearing lubricant can and frequently does result in bearing failure even though the bearing cavity contains an adequate volume of lubricant. Also, it is known that dirt or grit in contact with the primary seal can cause excessive seal wear which, in turn, can result in seal leakage and ultimate bearing failure. To overcome these problems, bearing seals conventionally employ a secondary or dust seal for excluding dust, grit, water and other foreign matter from contacting the primary lubricant seal. An example of a bearing seal including a primary sealing lip in contact with a seal surface on a seal case ring and a secondary or dust seal lip outboard of the primary seal lip also contacting the case ring seal surface can be found in U.S. Pat. Nos. 5,186,548; 4,432,557; and 4,106,781.
Seals are also known in which the elastomeric body forming the primary seal lip is formed to include lubricant slingers to act as pumping surfaces and reduce the pressure and/or volume of lubricant coming into contact with the primary seal lip. An example of such a seal may be found in U.S. Pat. No. 4,770,548. While such seals may be effective particularly for use in bearings lubricated with oils, they can produce excessive turbulence and increase lubricant temperature in the vicinity of the seal lip.
Labyrinth seals are also known. In such seals, as disclosed for example in U.S. Pat. No. 5,975,533, the radial thicknesses of thin annular gaps are generally such as to preclude the passage of grease-type lubricants therethrough during operation of the bearing.
In recent years, there has been an increased demand for bearing seals capable of reliably performing the sealing function over longer periods of time. This is particularly true, for example, in the trucking industry where in the past, it became standard practice to change the wheel bearing seals during each brake job. Even through the bearing seals may still have been doing their job effectively, the relatively low cost of individual seals and the danger of damage to a seal in removing and reinstalling the seal and the consequent bearing failure, replacing the seals with each brake job was considered economically sound. However, heavy-duty over-the-road trucks today make broad use of outboard mounted brakes, making it possible to complete a brake job without disturbing the bearing seals. Further, improved brake designs and materials have greatly increased the effective life of truck wheel brakes so that extended seal life is required even though some truck fleet operators may continue to follow the established practice of replacing seals at every brake reline. Thus, a long-life wheel bearing seal which will reliably and effectively maintain a seal, not only keeping the lubricant in the bearing but also excluding foreign materials, through the life of two or more brake linings is desired.
For a seal to reliably achieve such an extended life, it is not only critical that an adequate lubricant supply be maintained in the bearing, but it is particularly critical that foreign matter such as dirt, dust, road salt, water and other contaminants be excluded from the bearing lubricant since such contamination can cause bearing wear and failure when present even in very small quantities.
Accordingly, it is a primary object of the present invention to provide an improved bearing seal suitable for use in wheel bearings and the like. Preferably, the bearing is effective in sealing the bearing for extended periods of time. Another object is to provide such a seal which is efficient in maintaining the bearing lubricant in the bearing cavity and in excluding foreign material from the bearing.
In one aspect, the present invention provides a seal assembly for mounting on a shaft comprising a first ring-shaped seal case, a second ring-shaped seal case, and a ring-shaped elastomer body carried by the first seal case. The first and second seal cases and elastomer body have a central longitudinal axis. At least two of the first seal case, second seal case and elastomer body define a seal cavity. Portions of at least two of the first seal case, second seal case and elastomer body define a labyrinth seal radially spaced from the seal cavity. At least part of the second seal case is radially outward of the elastomer body and first seal case. The elastomer body includes a plurality of lips in contact with the second seal case at a position radially spaced from the seal cavity. At least part of the seal cavity is positioned between the labyrinth seal and the lips of the elastomer body. The labyrinth seal includes more than one axially directed gap.
In another aspect, the present invention provides a seal assembly for mounting on a shaft comprising a first ring-shaped seal case, a second ring-shaped seal case, and a ring-shaped elastomer body carried by the first seal case. The first and second seal cases and elastomer body have a central longitudinal axis. At least two of the first seal case, second seal case and elastomer body define a seal cavity. Portions of at least two of the first seal case, second seal case and elastomer body define a labyrinth seal radially spaced from the seal cavity. At least part of the second seal case is radially outward of the elastomer body and first seal case. The elastomer body includes a plurality of lips in contact with the second seal case at a position radially spaced from the seal cavity. At least part of the seal cavity is positioned between the labyrinth seal and the lips of the elastomer body. The labyrinth seal includes at least one axially directed gap and the elastomer body includes an axially directed lip defining part of the axially directed gap.
In another aspect, the present invention provides seal assembly for mounting on a shaft comprising a first ring-shaped seal case, a second ring-shaped seal case, and a ring-shaped elastomer body carried by the first seal case. The first and second seal cases and elastomer body have a central longitudinal axis. At least two of the first seal case, second seal case and elastomer body define a seal cavity. Portions of at least two of the first seal case, second seal case and elastomer body define a labyrinth seal radially spaced from the seal cavity. At least part of the second seal case is radially outward of the elastomer body and first seal case. The elastomer body includes a plurality of lips in contact with the second seal case at a position radially spaced from the seal cavity. At least part of the seal cavity is positioned between the labyrinth seal and the lips of the elastomer body. The labyrinth seal includes an interface between a radial face of the second seal case and a radial face of the elastomer body. The radial face of the elastomer body includes a plurality of raised chaplet surfaces nearest the radial face of the second seal case, a plurality of recessed surfaces spaced farthest from the radial face of the second seal case and a plurality of joining surfaces joining the raised chaplet surfaces and recessed surfaces. One of the seal cases is rotatable with respect to the other seal case.
In another aspect, the present invention provides a unitized seal assembly for sealing a bearing used to support a housing having a cylindrical bore therein for rotation relative to a journal on a shaft extending coaxially into the cylindrical bore to provide a sealed lubrication chamber for the bearing. The seal assembly comprises a first seal case in the form of a ring having a generally channel shape axial cross section. The first seal case includes a cylindrical mounting body portion terminating at each end in a generally radially extending flange. An elastomer body is carried by the first seal case and is bonded to at least part of the seal case. The elastomer body is molded to provide a primary seal lip spaced radially from the first seal case body portion. The elastomer body also has a pair of dust seal lips spaced axially from the primary seal lip and from one another. The seal assembly also includes a second seal case. The second seal case includes first, second and third radially spaced concentric cylindrical segments. The second and third cylindrical segments are joined at one end of the second seal case by a first generally radially extending portion. This radially extending portion is positioned radially between the radially extending flanges of the first seal case. The first and second cylindrical segments are joined at the other end of the second seal case by a second wall portion including a radially and axially inclined segment. The second cylindrical segment has a cylindrical sealing surface contacting the primary seal lip to define a primary lubrication seal. The inclined wall segment contacts at least one of the first dust seal lip and the second dust seal lip at a location spaced radially from the cylindrical sealing surface. The first seal case body is adapted to be mounted in fluid-tight relation on one of a shaft and a cylindrical recess supported for relative rotation by a bearing. The second seal case is adapted to be mounted in fluid-tight relation with the other of such shaft and cylindrical recess.
In another aspect, the present invention provides a unitary bearing seal mounted between a shaft and a bore in a relatively rotating member supported on the shaft by an antifriction bearing. The seal comprises a first annular seal case, an annular molded elastomer body and a second annular seal case. The first annular seal case has an elongated cylindrical body for mounting in lubrication-tight relation on a shaft. The cylindrical body includes a first radially outwardly extending flange at one end. The annular molded elastomer body is bonded onto at least part of the first seal case body. The elastomer body has integrally molded thereon a radially outwardly directed primary seal lip and at least one outwardly directed dust seal lip spaced axially from the primary seal lip. There is an axially extending, generally cylindrical groove defined at least in part by the elastomer body. The groove is positioned at a location spaced radially inward from the primary seal lip. The groove terminates in a generally radially extending end wall. The second annular seal case has a generally cylindrical mounting surface mounted in lubrication-tight relation in the bore of the relatively rotating member. The second seal case includes a generally cylindrical segment having a radially inward directed sealing surface contacting and forming a seal with the primary seal lip, and a generally cylindrical leg concentric with and spaced radially inward from the sealing surface and radially outward from the first seal case body. The leg extends into the annular groove and terminates in a generally planar, substantially radially extending end face. At least the leg of the second seal case and the groove cooperate to define a labyrinth seal. The second seal case further includes a generally radially extending wall joining the cylindrical segment and the leg, and another segment joining the cylindrical segment and the mounting surface. At least two of the first seal case, second seal case and elastomer body cooperate to define an annular seal lubricant cavity sealed by the primary seal lip and the labyrinth seal. The first seal case includes a substantially radially extending flange on the elongated cylindrical body opposite the first flange to maintain the seal in a unitized configuration. The leg of the second seal case is positioned between the flanges of the first seal case. The dust seal lip contacts at least one of the surfaces of the second seal case.